johnson analog contoller temp swing???

I hnave my analog johnson temp control all set up with my freezer, but the temp is ranging from 36 to 45. I have the temp probe in the freezer near the bottom in an empty glass with a thermometer sensor taped to it so I can gauge the temperature in the freezer. Maybe I am just missing something, but I don't get why the temperature swing is so big when it is supposed to be a 3.5 differential.
Thanks.

 

I'm guessing its because the probe is measuring the temp of the air, which will have greater temp swings (opening/closing of door, etc). Try taping the probe to a full glass of water or to your fermenter/keg to control that temp swing.

 

I will try that, thanks. But wouldn't the controller just kick on more often if it were measuring the more rapid temp changes of the air? I don't quite get why the range of temps is so big.

 

+1 Try the above (I bungee cord the probe to glass of water or carboy, but covering the probe with bubble wrap, pretty much sandwich the probe in between a sheet of the bubble wrap and against the glass...not wrapping the probe) Works great.

 

So does anyone else have this sort of temp swing? Is it possible that the thermostat is working correctly at a 3.5 degree differential and it stops the freezer from running at the right temp, but that the air temp continues to drop a little even after it stops running? It makes sense that just because the power is cut off, that the temp isn't going to instantly stay the same.

 

I wrote this too early this morning, so it isn't even on new posts anymore. Sorry for the bump...

 

Sure its plausible....best thing to do is insulate the probe from temperature swings, which you will have if the probe is measuring the temp of the air and the door keeps opening/closing.

Another thing to check...you have have the thermostat on the freezer set to its coldest temp?

Another plus to strapping the probe to the side of your fermenter....you'll be monitoring/controlling the temp of the fermenter, not the temp inside your freezer...this way you don't have to compensate by dialing down the freezer temp a few degrees in order to get the proper temp of your fermenter.